So what was behind the pair's decision to call off their engagement? According to a close source, Spears, 31, and Trawick, 41, both wanted "different things."

"There was no third party involved," says the source of the couple, who began dating in 2009. "Things haven't been ideal in their relationship for some time. There was a lot to work on before they could move forward and get married."

One of those things may have been Trawick's desire to maintain a life outside their relationship.

"Britney had a lot of issues with Jason doing his own thing – in business and seeing his friends," another source says. "In her perfect world he would have been home with her twenty-four/seven, so that was a point of contention; something they were always working on."

Another source of tension? Kids. "Britney wants to grow her family," says a source close to the couple. "Jason loves her boys but he is not in a place to have his own."

Though Spears recently purchased an $8.5 million mansion in L.A.'s Thousand Oaks neighborhood to live in with Trawick and her sons Sean, 7, and Jayden, 6, another source says everything wasn't picture perfect. "They've been spending a lot of time apart in the last few months," says the source.

While the pair's relationship had become "frustrating," according to the close source, they've put up a united front. Spears told PEOPLE exclusively in a statement Friday that she and Trawick are committed to remaining "great friends."

After hearing news of the split, a source who saw the couple and her children in recent weeks says, "They both seemed happy. Especially Britney, I could tell that she was in a really great place. She smiled a lot. They were both really at ease with the boys."

As Spears ends her relationship with Trawick – he also resigned as co-conservator over her person, which gave him authority to make decisions about her general well-being – the singer and former X Factor judge will return to doing what she loves: music.

"It's time for me to get back in the studio," she said in a statement Friday. "Watching [The X Factor contestants] all do their thing up on that stage every week made me miss performing so much! I can't wait to get back out there and do what I love most."